This invention relates to a holder intended for the detachable assembly of cutting tools, which comprises a housing and a clamping mechanism arranged therein.
A conventional clamping mechanism includes a male element arranged for engagement in a female-like opening in the tool, the male element being movable backwards and forwards in relation to a bushing included in the housing. The male element moves between an inner end position in which the tool is clamped in relation to the housing, and an outer end position in which the tool is detachable from the housing. The male element is moved by means of a piston which is movable backwards and forwards in a cavity inside the housing and which separates outer and inner chambers to and from which hydraulic oil may be fed in order to move the male element up against either of said end positions. The piston includes a projection with an outer, rearwardly converging first cone surface for co-operation with a number of tangentially spaced wedge bodies, which have inner, concavely arched surfaces for abutment against said cone surface on the piston projection. The wedge bodies also include a convexly arched surface for abutment against an inner, rearwardly diverging cone surface in said bushing. The first cone surface on the piston projection has a moderate cone angle with the purpose of bringing about self-locking of the piston device in the front end position thereof.
Tool holders of the above-mentioned type are generally found in automatic machines for chip forming machining such as turning, milling, drilling and the like. An advantage of this type of holder is that it permits fast and simple tool changing. A problem difficult to master in practice in previously known tool holders has, however, been to guarantee a distinct self-locking of the wedge bodies when the piston is brought to the rear end position thereof for fixing the tool in the holder. This self-locking of the wedge bodies, which relies upon the cone surface of the piston projection having a small cone angle, is required in order to be able to relieve the oil pressure in the chambers while keeping the tool secured during the periods when the tool is in operation.
Through investigations, on which the present invention is based, it has been proved that one reason for the difficulties in obtain a distinct self-locking of the wedge bodies after the oil pressure on the piston has been relieved, is that a thin oil film is present between the cone surface of the piston projection and the individual inner, concavely ached surface of the wedge body as a consequence of the fact that the piston projection as well as the wedge bodies are housed in a chamber which is permanently filled with oil. This means that the friction between said surfaces is reduced so much by the oil film that the self-locking effect does not come into effect immediately. That is, the tensile force, which the piston projection exerts on the wedge bodies and said male element when the tool is clamped, is not maintained once the oil pressure is relieved.
The present invention aims at obviating the above-mentioned problems in previously known tool holders and at providing a tool holder which, in a reliable way, can bring about a distinct self-locking of the wedge bodies in connection with the clamping of a tool; all with the purpose of guaranteeing that the tensile force which is exerted by the piston device in connection with the clamping is maintained without interruption, even after the oil pressure has been relieved.
According to the invention, the above-mentioned object is attained by a holder for the detachable assembly of cutting tools. The holder comprises a housing, a bushing, and a clamping mechanism. The housing includes an inner cavity defining a longitudinal center axis. The housing includes front and rear axial ends, the front end being adapted to receive a cutting tool. The bushing is disposed in the cavity and includes a surface which is inclined obliquely relative to the axis. The clamping mechanism is arranged in the housing and includes a clamping element, a piston, and a plurality of wedge bodies. The clamping element is adapted to be received in a cutting tool and is movable axially forwardly and rearwardly relative to the bushing between an axially rearward clamping position for clamping a cutting tool, and an axially forward unclamping position for unclamping the cutting tool. The piston is movable forwardly and rearwardly within the cavity and has an axial projection. The piston is arranged to divide the cavity into forward and rearward chambers to and from which hydraulic oil can be fed for moving the piston and the clamping element forwardly and rearwardly between clamping and unclamping positions, respectively. The wedge bodies are arranged around the piston projection for locking the piston in the clamped position. Each wedge body has radially inner and outer surfaces each being inclined obliquely relative to the axis. The piston projection includes an outer surface which is inclined obliquely relative to the axis and is arranged to engage the inner surfaces of the wedge bodies when the piston is moved rearwardly, to displace the wedge bodies radially outwardly and produce engagement between the bushing surface and the outer surfaces of the wedge bodies. The bushing surface is arranged for displacing the wedge bodies axially rearwardly in response to the engagement between the bushing surface and the outer surfaces of the wedge bodies. The clamping element is arranged to be forwardly and rearwardly displaced in response to forward and rearward movement, respectively of the piston. The outer surface of the piston projection has at least one groove formed therein and extending generally circumferentially therearound for evacuating oil from an interface between the outer surface of the piston and the inner surfaces of the wedge bodies.
Preferably, the groove lies in a plane oriented perpendicularly to the axis. There is preferably a plurality of the grooves, the grooves being axially spaced apart.